PVST+ in Multi-Vendor Networks

Some non-Dell Force10 systems which have hybrid ports participating in PVST+ transmit two kinds of BPDUs: an 802.1D BPDU and an untagged PVST+ BPDU (Cisco proprietary BPDU packet). The PVST+ BPDU is sent to perform consistency checking and to inform all other potential Cisco switches about the native VLAN configuration. Receiving switches consider only IEEE BPDUs (802.1D) for the native VLAN computations and ignore the SSTP (Shared Spanning Tree Protocol) BPDUs.

Force10 systems do not expect either tagged or untagged PVST+ BPDUs on an untagged VLAN so FTOS places the port in error-disable state by default when it receives this type of frame. This behavior, while consistent with other vendors, might result in the network not converging.

To resolve this issue, which is documented in PR 84608, FTOS Release 8.2.1.0 introduces a CLI option to set the error-disable state for receiving PVST BPDUs received on an untagged VLAN.

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Force10 (conf-if-gi-4/0)# no spanning-tree pvst err-disable cause invalid-pvst-bpdu

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The FTOS default remains placing the port in an error-disable state if a tagged or untagged PVST BPDU is received on an untagged VLAN.

Note: If VLAN 10 is untagged and an FTOS system receives a PVST BPDU with VLAN tag 20, the BPDU is simply dropped.